1. Field of the Invention
The present invention relates to an optical disc and a method of identifying a recording layer, and more particularly, to a recordable and/or reproducible optical disc, in which a physical address of smallest recording units and an address of the smallest recording units recorded during recording of data on the disc increase or decrease on first and second recording layers, and a method of identifying the recording layers without recording information about each recording layer.
2. Description of the Related Art
In an optical disc drive, physical identification data (PID) refers to information recorded for identifying a physical location on a disc whose data is to be reproduced. In general, PID is physical sector address information recorded on a recordable and/or reproducible medium on which data is recordable and/or reproducible per sector. PID is used to record data at an arbitrary position on a disc and to locate the recording position. A read-only memory (ROM) disc records addresses by using predetermined bits in an ID region of a header area of a sector that is the smallest unit of data that is recordable on a disc.
Referring to FIG. 1A showing a conventional parallel spiral track disc having dual layers, first and second layer L0-1 and L1-1 have the same track spiral direction. Here, as shown in FIG. 1B, sector addresses on the first and second layers L0-1 and L1-1 increase from an inner radius Rin of a disc to an outer radius Rout of the disc, respectively. In a case of continuous reproduction, data recorded on the first layer L0-1 of the disc is reproduced from the inner radius of the first layer L0-1 to the outer radius of the first layer and then data recorded on the second layers L1-1 of the disc is reproduced from the inner radius of the second layer L1-1 to the outer radius of the second layer L1-1. Because a pickup of a reproduction apparatus must move back toward the inner radius Rin of the disc in order to reproduce data from the second layer L1-1 successively after the first layer L0-1, an additional access time due to time for this movement as well as a decrease in linear velocity as shown in FIG. 1C is required.
To compensate for this, as shown in FIG. 2A, first and second layers L0-1 and L1-1 have opposite spiral directions. Furthermore, sector addresses on the first layer L0-1 increase from the inner radius Rin of the disc to the outer radius Rout, while sector addresses on the second layer L1-1 successively increase from the outer radius Rout to the inner radius Rin, thereby reducing a time taken to access from the first layer L0-1 to the second layer L1-1. This is called an opposite spiral track path. In particular, U.S. Pat. No. 5,881,032 discloses an optical disc in which sector addresses are arranged for a plurality of recording layers.
In a conventional DVD dual layer disc, first and second layers L0 and L1 are identifiable using predetermined bits in an ID region of a header area at the beginning of a sector that is the smallest unit that can be recorded on the disc. However, if a recordable disc is to store information about sectors and layers in a wobble on a groove track, repeated recording may degrade characteristics of the wobble so that the information about sectors or layers is not detectable. For example, a DVD-RAM stores address information including layer information in a header area in the form of pits before recording data. However, the layer information is repeatedly recorded in a data identification data (DID) region during actual recording. This is because physical addresses are needed for recording data and more reliable addressing is achieved. However, repeatedly recording the layer information results in overhead according to high density recording.
Thus, it is highly desirable to have a dual layer disc as a recordable and/or reproducible optical disc and to effectively record information other than user data for high density recording.